Asymmetric exchange bias training effect in spin glass (FeAu)/FeNi bilayers

A significant exchange bias (EB) training effect has been observed in sputter deposited FeAu/FeNi bilayers, wherein the exchange field (H-E) exhibits a special sign-changeable temperature dependence. Very interestingly, despite the absence of multiple easy axes in the FeAu spin glass (SG) layer, H-E drops abruptly between the first and second magnetic cycles, which is followed by a more gradual continuous change in the subsequent cycles. This training behavior cannot be described by the empirical n(-1/2) law because of the asymmetric magnetization reversal processes. We propose modifying Binek's model to include the asymmetric changes of the pinning SG spins at the descending and ascending branches. This new model successfully describes the EB training effect in FeAu/FeNi bilayers.